Our goal is to identify factors that regulate the generation and maintenance of T cell memory which will protect against influenza virus infection. In Aim 1, We will focus on defining memory CD4 subsets by their phenotype and location, investigating which can migrate to the lung to combat respiratory pathogens. We will then determine their functional potential ex vivo and after transfer to adoptive hosts. We will focus on analyzing their ability to confer protection against a lethal challenge with influenza. Then in Aim 2, we will identify factors which lead to generation of the distinct subsets both in vitro and subsequently in vivo. We will particularly focus on adjuvants and the proinflammatory cytokines they induce. Lastly, in Aim 3, we will identify the factors which positively or negatively regulate the long-term persistence memory CD4 T cell subsets in the lung and secondary lymphoid organs. Rapid recruitment of memory T cells into tissue sites where challenge with the priming antigen occurs, can be crucial for development of an efficient secondary effector response. Understanding the factors that control or enhance appropriate localization and response of memory T cells in general, and subsets of memory cells in particular, will be critically important for the future design of effective broad spectrum vaccines that provide long-lived protection. We will study memory generation in a well characterized model of response to influenza where identifiable naive TcR Tg CD4 T cells are transferred into intact hosts in which they respond to influenza infection. In humans the consequences of influenza infection range from mild to lethal, based mainly on the level of antibody protection afforded by prior exposure to virus. Antibody provides protection only against strains carrying the same hemagluttinin (HA) epitopes. Devastating epidemics have occurred when naturally occurring viral strains have emerged carrying new HA variants to which the population has not been previously exposed by infection or vaccination. A major concern is that such strains could also be produced by genetic engineering and could be used as agents of Bioterror. Fortunately, most T cell responses are not restricted to the variable epitopes and a vaccine strategy focusing on T cell immunity has the potential to provide protection against all or most potential strains and/or augment host responses sufficiently to prevent the worst consequences of a new influenza pandemic.